Devices of this type are used in, for example, the pharmaceutical industry to produce blister sheets, in which pockets for holding tablets must be formed. The thermoforming of sheets is used in many other industries as well.
Many different methods are available for thermoforming a sheet, including those based on the use of compressed air or a vacuum and those based strictly on forming over a male mold. When a sheet is thermoformed by means of compressed air, plug assists are used to guarantee uniform wall thicknesses and to support the forming process, depending on the type of sheet material, the thickness of the sheet, and the diameter/depth ratio of the pockets to be formed.
The plugs are heated so that the heated sheet does not cool down on contact with them. When thermoforming is carried out with compressed air, the plugs are located in the pressure space of the mold and are heated by means of cartridge heaters. This requires cable connections, which are subjected to bending stress as a result of the constant upward and downward movement of the plugs. If a cable breaks, the mold must be removed, and the defective parts such as cables or cartridge heaters must be replaced. Such failures are always unplanned and require that production be interrupted.